存储绘图画布并在以后恢复它 [英] Store drawing canvas and restore it later

问题描述

我做了我的Andr​​oid应用程序，用户可以画一些简单的白板。我想补充一个撤消功能，这样他就能够回到他的previous行动。

I've made a simple whiteboard on my Android app, where the user can draw something. I want to add an Undo feature so that he will be able to go back to his previous action.

在我的触摸开始事件，我已经添加了以下code基本上将当前画布上的的ArrayList ，并创建一个新的，以避免同样的参考。

On my Touch Start event, I've added the following code which basically adds the current canvas to an ArrayList and create a new one to avoid same reference.

previousDrawing.add(this.canvas);
this.canvas = new Canvas(this.bitmap);

然后，在我的撤消的方法，我已经添加了以下code：

Then, in my undo method, I've added the following code:

if (previousDrawing.size() > 0)
{
     // Remove last
    this.canvas = previousDrawing.remove(previousDrawing.size() - 1);
    this.canvas.setBitmap(this.bitmap);
}

它不会在所有的工作。我的意思是，我能够借鉴使用 this.canvas.drawPath（this.path，this.paint）我的画布; 而不是保存和恢复previous帆布。

It doesn't work at all. I mean, I'm able to draw on my canvas using this.canvas.drawPath(this.path, this.paint); but not to save and restore a previous canvas.

你能帮我做到这一点？

先谢谢了。

编辑：
我也tryied使用 saveLayer方法。但是，当我救，我不再能够在画布上绘制。这是一种正常的行为？

EDIT : I've also tryied to use the saveLayer method. But when I save, I'm no longer able to draw on the canvas. Is this a normal behaviour ?

推荐答案

尝试 drawBitmap 而不是 setBitmap

this.canvas.drawBitmap（this.bitmap，0，0，NULL）;

修改

if (previousDrawing.size() > 0)
{
     // Remove last
    this.bitmap = previousDrawing.get(previousDrawing.size() - 1);
    this.canvas.drawBitmap(this.bitmap, 0, 0, null);
    previousDrawing.remove(previousDrawing.size() - 1);
}

参考<一个href=\"http://developer.android.com/reference/android/graphics/Canvas.html#drawBitmap%28int%5B%5D,%20int,%20int,%20float,%20float,%20int,%20int,%20boolean,%20android.graphics.Paint%29\"相对=nofollow>链接

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